Inflammatory bowel diseases (IBD) is a so-called intractable disease which its cause is unknown, and which involves chronic inflammation or ulcer of the mucosae of the large intestine and small intestine, persistent diarrhea and bloody stool for a long period of time, and recurrence of the symptoms. In Japan, IBD is designated as a “specified disease” (i.e., specified rare and intractable disease), and as part of the research projects for combating against such specified diseases, specified-disease recipient certificates are issued to patients suffering IBD. Two typical IBDs are Crohn's disease (CD) and ulcerative colitis (UC).
Crohn's disease, which is also called regional colitis, granulomatous ileitis, or ileocolitis, is a chronic inflammatory disease of intestinal wall and occurs at any site of the gastrointestinal tract. Ulcerative colitis is a chronic inflammatory disease involving inflammation of the large intestine resulting in ulcer formation, with symptoms of hemorrhagic diarrhea, severe abdominal pain, and attack thereof with fever. Although the patients of both diseases are more numerous in Europe and America than in Japan, the number of the patients has continuously increased in Japan. According to the statistics of 2001, there were about 73,000 ulcerative colitis patients, and about 21,000 Crohn's disease patients in Japan. Among 46 specific diseases, ulcerative colitis was first in the number of recipient certificate issues, and Crohn's disease was eighth.
Since the cause of inflammatory bowel disease, as described above, has not been identified, conventional therapeutic drugs for diarrhea and similar drugs are not effective to IBD. Instead, in the treatment of inflammatory bowel disease, an aminosalicylic acid drug (sulfasalazine, 5-aminosalicylic acid) and a corticosteroid drug have widely and conventionally been employed as drugs of first and second choice, respectively. In the case of severe IBD, an immunosuppressive agent (azathioprine, 6-mercaptopurine, etc.) or an anti-cytokine drug is also employed. As an aminosalicylic acid drug, sulfasalazine and 5-aminosalicylic acid are widely employed. However, about 50% of the patients who have taken an aminosalicylic acid drug complain of onset of gastrointestinal disorders such as nausea, vomiting, inappetence, and liver function disorders; and hematologic system disorders such as granulocytopenia, hemolytic anemia, and folic acid deficiency anemia. In addition, since aminosalicylic acid drugs have a salicylic acid skeleton, a patient having anaphylaxis to a salicylic drug may complain of adverse side effects, such as diarrhea, abdominal pain, rise in amylase level, and kidney disorders. Sulfasalazine causes adverse side effects such as male sterility and urine coloration, which impose large stress on the patients. Corticosteroid drugs cause various adverse side effects such as osteoporosis, growth disorders, secondary adrenal failure, impaired glucose tolerance, and hypertension, and are not effective for maintenance of remission in CD or UC, which are problematic. On the other hand, anti-cytokine therapy is a new therapy completely differing from conventional therapies. The first anti-cytokine drug is infliximab, which is a chimeric anti-human TNF-α monoclonal antibody. Infliximab is known to be effective for patients of medium to severe Crohn's disease having steroid resistance (Non-Patent Document 1), and for maintenance of remission in the target disease (Non-Patent Document 2). Known adverse side effects of infliximab include hypertension, chills, exanthem, fever, headache, and eczema. In addition, since infliximab is a chimeric antibody, it may be antigenic. In this case, acute super anaphylaxis may occur. Infliximab may cause infection which requires an antibiotic drug for the treatment thereof, and may exhibit carcinogenicity, which are also problems recognized recently.    Non-Patent Document 1: N. Engl. J. Med., vol. 337, p. 1029, 1997    Non-Patent Document 2: Gastroenterology, vol. 117, p. 761, 1999